萝莉的烦躁期The freedom of twist-separation is very useful in practical applications.The twist-four operator in the cut-o?scheme is quite complicated,not suitable for non-perturbative meth-ods.In what follows,I seek a de?nition of the twist-four operator convenient for lattice calculations,because the lattice is the only practical means at present for a non-perturbative calculation.Following the de?nition,I calculate the corresponding twist-two coe?cient func-tion.The approach here can be generalized straightforwardly to the application of the OPE to the QCD sum rules,which will be discussed in a separation publication[30].
I choose to de?ne composite operators in Euclidean space,in which the lattice realization is usually made.Imagine the space-time is discretized into a lattice with hypercubes;the lattice spacing isπ/Λ.The quark?elds are assigned at every lattice point and gluon?elds are represented by gauge links with
Uµ(n)=P e?ig(π/Λ) 10Aµ(n+x?µ)dx(22)
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